Do not allow to create more answers than the maximum defined

In case we receive consecutive requests we are locking the poll author record
until the first request transaction ends, so the author answers count during
subsequent requests validations is up to date.

app/models/poll/answer.rb

@@ -7,6 +7,7 @@ class Poll::Answer < ApplicationRecord
   validates :question, presence: true
   validates :author, presence: true
   validates :answer, presence: true
+  validate :max_votes
 
   validates :answer, inclusion: { in: ->(a) { a.question.possible_answers }},
                      unless: ->(a) { a.question.blank? }
@@ -21,4 +22,16 @@ class Poll::Answer < ApplicationRecord
       Poll::Voter.find_or_create_by!(user: author, poll: poll, origin: "web")
     end
   end
+
+  private
+
+    def max_votes
+      return if !question || question&.unique? || persisted?
+
+      author.lock!
+
+      if question.answers.by_author(author).count >= question.max_votes
+        errors.add(:answer, "Maximum number of votes per user exceeded")
+      end
+    end
 end

spec/models/poll/answer_spec.rb

@@ -23,6 +23,30 @@ describe Poll::Answer do
       expect(answer).not_to be_valid
     end
 
+    it "is not valid when user already reached multiple answers question max votes" do
+      author = create(:user)
+      question = create(:poll_question_multiple, :abc, max_votes: 2)
+      create(:poll_answer, author: author, question: question, answer: "Answer A")
+      create(:poll_answer, author: author, question: question, answer: "Answer B")
+      answer = build(:poll_answer, author: author, question: question, answer: "Answer C")
+
+      expect(answer).not_to be_valid
+    end
+
+    it "validates max votes when creating answers at the same time", :race_condition do
+      author = create(:user, :level_two)
+      question = create(:poll_question_multiple, :abc, max_votes: 2)
+      create(:poll_answer, question: question, answer: "Answer A", author: author)
+      answer = build(:poll_answer, question: question, answer: "Answer B", author: author)
+      other_answer = build(:poll_answer, question: question, answer: "Answer C", author: author)
+
+      [answer, other_answer].map do |a|
+        Thread.new { a.save }
+      end.each(&:join)
+
+      expect(Poll::Answer.count).to be 2
+    end
+
     it "is valid for answers included in the Poll::Question's question_answers list" do
       question = create(:poll_question)
       create(:poll_question_answer, title: "One", question: question)